Filter material for a fluid and drainage layer for such a filter material including a filter element

ABSTRACT

The invention relates to a filter material for a fluid, in particular in the form of a hydraulic fluid, said filter material comprising a multi-layer filter medium ( 10 ) through which a fluid can flow and which has at least one filter layer ( 20 ), a drainage layer ( 32 ) which forms a three-dimensional structure being designed to enlarge the flow channels formed for the fluid to flow through. Said drainage layer cooperates with an adjacent drainage layer and/or consists of individual line elements ( 33 ) that form a mesh or grid structure, those line elements being arcshaped or curved at least to some extent. The invention further relates to a drainage layer ( 32 ) as such and to a filter element based thereon.

The invention relates to a filter material for a fluid, in particular inthe form of a hydraulic fluid, which has a multi-layer filter medium,through which a fluid can flow, and which has at least one filter layer.The invention furthermore relates to a drainage layer, in particularprovided for such a filter material, and to a filter element made withsuch a filter material.

Filter materials for producing replaceable filter elements in hydraulicsystems are known in many different designs (US 2005/0269256 A1, US2007/0175191 A1, etc.) and comprise, for example, a nonwoven filter,preferably composed of multiple layers, having a support layer on one,but preferably on both sides (upstream and/or downstream side). Whenfluid flows through the filter material, considerable pressuredifferences result to some extent between the raw side and the cleanside.

To be able to withstand these pressure differences and also dynamic flowforces in the unfiltrate, the filter materials, of which correspondingfilter elements are made, have so-called support layers. Such supportlayers or support structures are subject to an alternating pressure loadduring operation of the filter element. Known support structures can beformed of metal fabrics, in particular fabrics made of high-grade steelwires, which prove to be particularly stable. In the prior art, suchfabrics are executed as standard fabrics (DE 600 34 247 T2), also in themanner of a so-called plain weave, wherein the threads are always wovenso as to alternate above and then again below the next thread. Knownfilter materials having support layers and filter layers formed in thismanner do not satisfy the requirements placed on them with regard tofluid permeability, which is as high as possible, with high mechanicalstability, even if, in addition to support layers and filter layers, afluid-guiding drainage layer is provided in the form of a grid orfabric, both on the fluid upstream as well as on the fluid downstreamside of the filter material, or if larger mesh sizes or coarser gridsare provided, so as to obtain lower flow resistances. The latter casesresult in the disadvantage of the lower resilience against alternatingpressure loads during operation.

With regard to this problem, the object of the invention is to provide afilter material that ensures a high fluid-permeability despite goodstructural strength.

According to the invention, this object is achieved by means of a filtermaterial, which in each case has the features of claim 1 and of claim 4in its entirety, by means of a drainage layer according to the featuredesign of claim 18 as well as by means of a filter element according tothe feature design of claim 20.

According to the content of claim 1, an essential feature of theinvention is that, in the layer composite of the filter material, inaddition to at least one first drainage layer, which can also be formedfrom a support layer or a support grid, an additional drainage layer,forming a three-dimensional structure, is provided, in order to enlargethe flow channels formed for the fluid flowing through it. On the onehand, an additional three-dimensional structure effects the creation ofadditional flow channels, which leads to a decrease in the pressuredifferential, in particular on the downstream side of the filtermaterial, where very narrow flow channels are created due to a starfolding of the filter material. On the other hand, an increasedresilience against alternating pressure loads also results on theupstream side of the filter material due to the stabilizing of thepleats by decreasing the pleat spacings, as it results from the presenceof the drainage layer. Due to the formed additional flow channels of theadditional further drainage layer, the pleat spacings of the pleatedfilter mat or of the pleated filter medium are decreased, which leads toan additional stabilization of the individual pleats. It has proven tobe particularly advantageous if the additional drainage layer is flushwith an adjacent drainage layer.

According to the content of claim 4, an essential feature of theinvention is that the drainage layer, which is provided for increasingthe fluid flow and which forms a three-dimensional structure with theline elements, which are used and which form the mesh or grid for thedrainage layer, are arc-shaped or curved, at least to some extent. Thiscreates a particularly high structural stability for this drainage layerand therefore for the entire filter medium in a desired manner, andadditional flow channels having a particularly large cross section arefurthermore created, which leads to a decrease of the pressuredifferential, in particular on the downstream side of the filtermaterial, where very narrow flow channels are created due to the commonstar folding of the filter material. The fact that, due to being curved,a helical guide for the fluid is obtained, also contributes to this,which leads to an energy input having improved flow through the filtermedium.

On the other hand, an increased resilience to alternating pressure loadsresults due to the stabilizing of the pleats by decreasing the pleatspacings on the upstream side of the filter material, as follows fromthe presence of the drainage layer having the curved, helical arcs forthe line elements.

In the case of a preferred embodiment of the solution according to theinvention, two line elements, which run adjacent to one another in anarc-shaped manner at least to some extent, are provided to define a flowchamber between two consecutive cross points such that the largestopening width of said flow chamber is formed between two apexes of thecurved course, which are spaced apart from one another. Preferably,provision is made thereby for said flow chamber to be shaped asapproximately circular, elliptical or in the manner of a rhombus,between two adjacent curved courses. A particularly good compromise withregard to good stability characteristics and high fluid permeability canbe realized thereby, wherein the flow chambers form individual flowchannels, which, being defined by the line elements, provide for anoptimal, helical flow guide within a filter element that is equippedwith the filter material according to the invention.

Particularly preferably, provision is furthermore made for at least onesupport layer to be composed of line-shaped grid or mesh elements, whichborder individual outlets at the edges thereof. In this respect, aparticularly good support for the entire filter material or filtermedium is then attained by means of the arc-shaped courses of theline-shaped elements of the drainage layer. In this regard, therespective support layer assumes the function of a common first drainagelayer, which interacts with the additional drainage layer, preferably inthe case of a flat arrangement.

Further advantageous embodiments of the filter material according to theinvention are the subject matter of the other dependent claims.

According to the content of claim 18, a drainage layer, in particularprovided for the above-described filter material, is also the subjectmatter of the invention, wherein the individual line elements of thedrainage layer are arc-shaped or curved at least to some extent, which,particularly preferably, are arranged within a repeating pattern so asto be curved in an S-shape at least to some extent.

According to the content of claim 20, the filter element, which isprovided for use in a filter device for fluid, in particular forhydraulic fluid, and which has a filter material according to one ofclaims 1 to 17, and particularly preferably a drainage layer accordingto claims 18 and/or 19 is also subject matter of the invention.

The invention shall be explained in detail below, based on the drawings.Therein:

FIG. 1 shows the upper part of a filter element having a filter materialaccording to the prior art in a partially sectional, schematicallysimplified drawing;

FIG. 2 shows an enlarged top view of a partial area of a filter materialaccording to the prior art;

FIG. 3 shows a top view, similar to that of FIG. 2, of a filter materialaccording to an exemplary embodiment of the invention;

FIG. 4 shows an enlarged, perspective diagonal view of only a partialarea of the filter material, which adjoins pleat tips, according to theexemplary embodiment of FIG. 3 and

FIG. 5 shows a top view of a second exemplary embodiment of the filtermaterial, which is similar to FIG. 3.

The filter element partially illustrated in FIG. 1, as it belongs to theprior art, has a filter mat 10 as the filter material, having apredefinable surface area and predefinable filter characteristics. Thefilter mat 10 is pleated, as illustrated in FIG. 1, with individualfilter pleats 12, which, in a tight package sequence, extend between aninner fluid-permeable support tube 14 and an outer cylindrical housingshell 16, which is likewise fluid-permeable. For the sake of a betterdepiction, the individual filter pleats 12 are depicted slightly pulledapart, and the individual layer structure of the pleated filter mat 10is revealed from the partial depiction facing the observer. The filterpleats 12 form a W-shape or V-shape and define fluid gaps between oneanother, the volume of which increases towards the upstream side, whichis directed outward.

In the case of filter elements, which are constructed in such a mannerthat the filter mat 10 typically comprises a first support layer 18, asecond layer 20 as protective nonwoven, a third layer 22 as mainnonwoven or filter layer, optionally a further, likewise adjoining, notdepicted, layer of a protective nonwoven, or further filter layer and,in any event, a fourth layer of a new support layer 24, which runs onthe inner circumference. Said support layers 18, 24 can consist of awire fabric, a plastic grid or a plastic fabric, among others. One ofthe layers can additionally be used as drainage layer. The protectivenonwoven layers 20 are routinely composed of a plastic nonwoven, and themain nonwoven or filter layers 22 are composed of materials such asglass fiber paper, synthetic filter material (melt-blown fibers),cellulose paper, or the like. Said layers can also be made of so-calledcomposite materials of the same or of different types. As a function ofthe layer structure and of the respective used filter materials, thefilter mat 10 has predefinable filter characteristics, in accordancewith the filtration task, wherein, on principle, a high pressuredifferential stability is desired, as well as a high beta stabilityacross a wide pressure differential range, as well as predefinablefilter fineness, wherein sufficient flow channels should be available atthe filter element for decreasing the pressure differential, while agood resilience against changing compressive loads should be ensured atthe same time.

Seen from the perspective of FIG. 1, the fluid flows through the filtermat 10, in the case of the known filter element, from the outside(upstream side) to the inside (downstream side) and is supported on theinner circumference at its respective pleat deflections against theouter circumference of the support pipe 14 with its annular apertures.However, it is also possible for the fluid, which is to be cleaned, toflow through differently designed filter elements in the reversedirection, so that the above-mentioned upstream side becomes thedownstream side and vice versa. The filter mat ends are, in each case,accommodated in an end cap, wherein only the upper end cap 26 isillustrated partially in FIG. 1, which incidentally comprises aspring-loaded bypass valve 28, which, for safety reasons, makes itpossible for a fluid to pass through, even if the filter mat 10 shouldbe clogged, thus blocked by contaminants.

FIG. 2 shows a top view of a filter material in the form of a filter mat10 according to the prior art, having a standard support layer 24, whichis formed by means of a metallic grid. Such a grid, optionally having afurther inner support layer, which is not visible in FIG. 2, serves asdrainage layer, so as to create flow channels for allowing the fluid toflow through.

In contrast, the exemplary embodiment of the filter material accordingto the invention shown in FIG. 3 differs therefrom in that a drainagelayer 32, which is also referred to as an additional drainage layer 32,is provided for an additional drainage function by forming enlarged flowchannels. To provide such additional flow channels in the area of thedownstream side of the filter mat 10, the drainage layer 32 is provideddirectly below the outer support layer 24 in the exemplary embodiment ofFIG. 3, where the downstream side of the filter mat 10 is visible. Tocreate clearances, this drainage layer 32 is a three-dimensionalstructure element, and in the present example, a grid-like structuremade of plastic, for example of polybutylene terephthalate,polypropylene or polyester, is provided. A metallic fabric or plasticfabric, which, can provide for an electric voltage discharge, canlikewise be provided.

In addition to the drainage effect, the drainage layer 32, which isdisposed on the inside in the case of the exemplary embodiment of FIGS.3 and 4, contributes to the pleat stabilization. As can be derived fromFIG. 4, the additional volume of the drainage layer 32, which representsa three-dimensional formation, has the result that the filter pleats 12adjoin the pleat tips of the upstream side more closely with smallerspacings 34 (see FIG. 4). The additional drainage layer 32 thus alsoforms a further support layer for the filter mat 10.

In the case of the exemplary embodiment of FIG. 5, the drainage layer 32is disposed as an outer layer on the downstream side of the filter mat10. In the case of the depicted example, the drainage layer 32 is formedby means of an irregular grid structure made of plastic. When disposedon the downstream side of the filter mat 10, where very narrow flowchannels result due to the star folding (pleating), the drainage layer32 makes a particularly effective contribution to decreasing the flowresistance and thus the pressure differentials, which are created duringoperation.

As is shown in particular in FIG. 5, at least the line elements 33 ofthe drainage layer 32 are provided with an arc-shaped or curved course.In particular, the arc-shaped or curved course within a repeatingpattern, in the case of which the weave pattern repeats, is embodied inthe manner of S-shaped line elements 33. Between two consecutive crosspoints 35, two line elements 33, which run adjacent to one another in anarc-shaped manner, define a flow chamber 37, the largest opening widthof which is between two apexes 39, which are spaced apart from oneanother, of the arc-shaped courses. The flow chamber 37 formed in thismanner, between two adjacent curved courses of the line elements 33, isembodied thereby, approximately, in the manner of an ellipsis or of arhombus.

Provision is furthermore made that, at the cross points 35, in the caseof which the arc-shaped line elements 33 rest against one another, ontop of one another, said curved line elements in each case form an angleα, which changes continuously within predefinable angle limits within arepeating pattern, increasing continuously downwards, in particular whenseen from the perspective depicted in FIG. 5.

The support layer 18 or 24, which is disposed thereunder, is formed ofline-shaped grid or mesh elements 41, which border on individual outlets43 for the fluid at the edges. The outlets 43 of the respective supportlayers 18, 24 have a rectangular or rhombic shape thereby; in the shownexemplary embodiment according to FIG. 5 in the manner of a rectangle.

The flow chambers 37 of the drainage layer, in turn, are designed in themanner of channel-like flow guides, which are bordered, at least to someextent, on the edge side by the line elements 33, which run in anarc-shaped manner. Helically formed flow channels, which ensure animproved fluid entry into the other layers of the filter material,including the respective support layer 18, 24 thereof, are created insuch a way. Particularly preferably, provision is thereby made for thefree flow cross section of the flow chambers 37 of the drainage layer 32to be dimensioned to be equal to or preferably larger than, particularlypreferably twice as large as, the flow openings 43 of the support layer18 or 24 located thereunder.

The individual line elements 33; 41, which are connected to one anotherin a mesh-shaped manner, of drainage layer 32 or of the respectivesupport layer 18 or 24, respectively, are embodied as filaments,threads, yarns or fibers made of plastic and/or metal materials and arepart of a screen, braided fabric, knitted fabric, fabric or, asillustrated, in the form of a mesh-like grid.

As already specified, the drainage layer 32 can support itself directlyat a support grid 18 or 24, which can be assigned thereto, in that theline elements 33; 41 are in direct contact with one another at least tosome extent. However, it is likewise possible to dispose the drainagelayer 32 between two other layers, preferably between a further drainagelayer (not depicted) in the layer composite and one of the supportlayers 18, 24. In particular, provision can also be made to not onlyarrange the drainage layer 32 on the downstream side within the filtermaterial, but instead also on the upstream side. Particularlypreferably, however, the drainage layer 32 is disposed on the downstreamside, upstream of the inner further support layer 24, wherein this kindof drainage layer 32 can additionally or alternatively also be disposedin the outermost area, in the flow direction upstream of the firstsupport layer 18.

As specified above, the mentioned drainage layer 32, together with thefilter material described therein, can be combined to form a filterelement in accordance with the depiction in FIG. 1. However, it is alsopossible to use the drainage layer 32 as an independent component withother filter media or filter materials, also in non-pleated form, for afluid filtration, also in the form the beverage filtration.

1. A filter material for fluids, in particular hydraulic fluids, whichhas a multi-layer filter medium (10), through which a fluid can flow,and which has at least one filter layer (20) as well as at least onedrainage layer, characterized in that an additional drainage layer (32)is provided, which forms a three-dimensional structure, to enlarge theflow channels formed for the fluid to flow through.
 2. The filtermaterial for fluids according to claim 1, characterized in that theadditional drainage layer (32) is disposed on the fluid downstream sideof the filter material.
 3. The filter material for fluids according toclaim 1, characterized in that the additional drainage layer (32) isflush with an adjacent drainage layer.
 4. A filter material for a fluid,in particular in the form of a hydraulic fluid, having a multi-layerfilter medium (10), through which a fluid can flow, and having at leastone filter layer (20), wherein a drainage layer (32) is provided, whichforms a three-dimensional structure, to enlarge the flow channels formedfor the fluid to flow through and which is composed of individual lineelements (33) forming a mesh or grid structure, characterized in thatthe line elements (33) are arc-shaped or curved, at least to someextent.
 5. The filter material according to claim 4, characterized inthat two line elements (33), which run adjacent to one another, in anarc-shaped manner at least to some extent, define a flow chamber (37)between two consecutive cross points (35), with the largest openingwidth of said flow chamber being formed between two apexes (39) of thearc-shaped courses, which are spaced apart from one another.
 6. Thefilter material according to claim 4, characterized in that the flowchamber (37) is shaped as approximately circular, elliptical or in themanner of a rhombus between two adjacent arc-shaped line elements (33).7. The filter material according to claim 4, characterized in that, atthe cross points (35), in the case of which the arc-shaped line elements(33) rest against one another, on top of one another, said arc-shapedline elements form an angle (α), which changes continuously withinpredefinable angle limits within a repeating pattern.
 8. The filtermaterial according to claim 4, characterized in that at least one of thesupport layers (18, 24) is comprised of line-shaped grid or meshelements (41), which border individual outlets (43) for the fluid at theedges and which in each case form a drainage layer.
 9. The filtermaterial according to claim 4, characterized in that the outlets (43) ofthe respective support layers (18, 24) are rectangular or rhombic inshape.
 10. The filter material according to claim 4, characterized inthat the flow chambers (37) are designed in the manner of channel-likeflow guides, which are bordered, at least to some extent, at the edgesby the line elements (33), which run in an arc-shape.
 11. The filtermaterial according to claim 4, characterized in that the flow crosssection of the flow chambers (37) of the drainage layer (32) isdimensioned to be equal to or preferably larger than, particularlypreferably twice as large as, the flow openings (43) of the respectivesupport layer (18, 24).
 12. The filter material according to claim 4,characterized in that the individual line elements (33; 41) of thedrainage layer (32) and/or support layer (18, 24), designed asfilaments, threads, yarns or fibers made of plastic and/or metalmaterials, which are connected to one another in the manner of a mesh,are part of a screen, braided fabric, knitted fabric, or grid.
 13. Thefilter material according to claim 4, characterized in that the drainagelayer (32) is supported directly at a support grid (18, 24), which canbe assigned thereto, in that the line elements (33; 41) are in directcontact with one another, at least to some extent.
 14. The filtermaterial according to claim 4, characterized in that the drainage layer(32) is arranged between two other layers, preferably between a furtherdrainage layer in the layer composite and one of the support layers (18,24).
 15. The filter material according to claim 4, characterized in thatthe drainage layer (32) having the line elements (33), which run in anarc-shape, is disposed as an outer layer of the layer composite on theupstream side.
 16. The filter material according to claim 4,characterized in that the diameter for the individual line elements (33)of the drainage layer (32) is selected to be greater than the diameterof the line-shaped grid or mesh elements (41) for the respective supportlayer (18, 24).
 17. The filter material according to claim 4,characterized in that the layer structure in the flow direction of thefluid through the filter medium (10), viewed from outside to inside, hasthe following structure: additional drainage layer (32), at least oneadjacently disposed drainage layer and/or support layer (18), at leastone filter layer (20), at least one further drainage layer and/or, as analternative to this, further drainage layer, at least one furthersupport layer (24).
 18. A drainage layer, in particular provided for afilter material according to claim 4, which is composed of individualline elements (33) forming a mesh or grid structure, characterized inthat the individual line elements (33) are arc-shaped or curved, atleast to some extent.
 19. The drainage layer according to claim 4,characterized in that the line elements (33) of the drainage layer (32)assume an S-shaped course within a repeating pattern of the grid or ofthe mesh structure.
 20. A filter element, which is provided for use in afluid device for fluids, in particular for hydraulic fluids, and whichhas a filter material according to claim 1 and/or a drainage layer.